Bolts are frequently used in construction projects and daily maintenance, and they play a key role in stability and safety, so choosing the right type of bolt is particularly important. Bolts are designed for different usage scenarios, from head shape to thread pattern. This article will delve into the world of bolts, analyzing their types, materials, and key applications.
Key Bolt Types and Their Unique Features
Hex Bolts
Hex Head Bolts also known as Hex Cap Screws, are fasteners with a hexagonal head made of medium to high carbon steel (strength grade 4.8-12.9), usually used with a nut, fit a spanner or wrench allowing you to tighten the screw.
Dimension standards:
Metric: Follow ISO 4014 (full thread), ISO 4017 (half thread).
American: Distinguish between UNC (coarse thread) and UNF (fine thread).
There are a variety of surface treatments to choose from:
Galvanized, Nickel Plating, Dacromet, Phosphating, Black Oxide.
High torque resistance due to the hexagonal grip, ideal for heavy-load scenarios.General-purpose fastening in machinery, construction beams, and automotive frames.
Socket Head Cap Screws
Socket Head Cap Screws, also known as Allen Head Screws, are cylindrical heads with low height design to save installation space. The top has a hexagonal groove, which can provide high torque transmission capacity and prevent thread slippage. The stem is a full-thread or half-thread design and needs to be installed with an Allen key. The head diameter is about 1.5 times the room temperature diameter. The materials include carbon steel, stainless steel, alloy steel, etc.
Size Range:
Metric: M1.6 to M64 (diameter), 3mm to 500mm length.
Imperial: 0.0625" to 2.5" (diameter), 1/8" to 20" length.
According to different application methods, you can choose Black Oxide, Nickel Plating and Zinc Plating and other surface treatment methods. It is mainly suitable for precision instruments, 3C products, and mold fixation.
Round Head Bolts
Round head bolts (button head) have a hemispherical smooth head, no edges and corners, are scratch-resistant, and have high safety. They are similar to carriage bolts, but do not have a square neck under the bolt head. Since round head bolts are used for wood connections, their strength is usually not high and they meet the ASTM A307 standard.
Typical applications: wooden structures, outdoor furniture, amusement facilities
Flat Head Bolts/Countersunk Bolts
Countersunk/Flat Head Hex Socket Screws, available in hex or allen drive styles, with conical heads that are low-profile and flush with the material surface after installation. Their streamlined appearance can reduce wind resistance or motion interference.
Metric: Diameter M2 - M30, Length 4mm - 300mm
Imperial: Diameter #0-80 - 1-1/4", Length 1/8" - 8"
Fully threaded design is suitable for ship decks, aircraft skins, high-end furniture
T-bolts
T-head bolts (T-slot bolts) are also called T-slot bolts. They are fasteners with a T-shaped head. The bolt is inserted into the groove and can be rotated 90° to lock after sliding along the groove. They are designed to fit T-slots (such as machine tool workbenches or aluminum profile grooves) to prevent rotation.
The threads are usually full or partial threads, with a variety of materials and flexible lengths to fit different groove depths.
Commonly used in the construction and automotive industries, machine tools, automation equipment and modular assembly systems.
Carriage Bolts
A carriage bolt is a
T-bolts
T-head bolts (T-slot bolts) are also called T-slot bolts. They are fasteners with a T-shaped head. The bolt is inserted into the groove and can be rotated 90° to lock after sliding along the groove. They are designed to fit T-slots (such as machine tool workbenches or aluminum profile grooves) to prevent rotation.
The threads are usually full or partial threads, with a variety of materials and flexible lengths to fit different groove depths.
Commonly used in the construction and automotive industries, machine tools, automation equipment and modular assembly systems.
Carriage Bolts
A carriage bolt is a fastener with a square shoulder under a round head. Its square cross section provides enough grip to prevent rotation, which makes the bolt self-locking when passed through a square hole in a metal band. This allows the fastener to be installed from one side with only one tool (a spanner or wrench).
Carriage bolts are designed to pass through iron reinforcement plates on both sides of a wood beam. The square cross section of the bolt matches the square hole in the iron structure. It is commonly used on bare wood, but can also be used to build docks, swing sets, decks, and other places where a smooth surface is required.
fastener with a square shoulder under a round head. Its square cross section provides enough grip to prevent rotation, which makes the bolt self-locking when passed through a square hole in a metal band. This allows the fastener to be installed from one side with only one tool (a spanner or wrench).
Carriage bolts are designed to pass through iron reinforcement plates on both sides of a wood beam. The square cross section of the bolt matches the square hole in the iron structure. It is commonly used on bare wood, but can also be used to build docks, swing sets, decks, and other places where a smooth surface is required.
Eye Bolts
Eye Bolts are also called ring bolts. They are bolts with an annular eye on the top. The threaded shaft and the head form a ring (closed or open), made of carbon steel or stainless steel. The thread is full or partial, and the surface can be hot-dip galvanized or coated with Dacromet.
They are used for hanging, hoisting or pulling heavy objects.
U-Bolt
U-Bolt is also known as pipe clamp bolt, which has a round bend. The radius is adapted to the outer diameter of the pipe. It is usually semicircular or square bend. It has threads at both ends with nuts and washers to provide uniform clamping force for fixing round objects (such as pipes and cables).
Specifications: Match according to pipe diameter (such as DN50 pipe with Φ50 U-Bolt).
Material and surface treatment
Material: carbon steel (Q235B), stainless steel (304/316),
Surface treatment: galvanized (outdoor rust prevention), sprayed (color identification), passivated (stainless steel anti-fingerprint).
Main use: fixing of pipes
J-Bolts
J-Bolts are also known as J-type anchor bolts and anchor bolts. They are bolts with a J-shaped hook at one end, used to embed concrete or fix to the wall. They increase the mechanical bite force with concrete. They have no bolt head, but the threaded end can be installed with a nut. They are commonly used in the construction industry.
Material and surface treatment
Material: low carbon steel (easy to weld), stainless steel (resistant to underground corrosion).
Surface treatment: hot-dip galvanizing (resistant to soil corrosion), epoxy coating (acid and alkali environment).
Main uses:
Foundation anchoring: embedded in the equipment foundation
Wall fixing: guardrail column, solar bracket.
Lag bolts
Lag bolts are often called lag screws. Lag bolts are different from other bolts. They look like screws rather than bolts, stout bolts with hexagonal heads and widely spaced threads, but they end in a pointed head instead of the blunt head common on most bolts.
Lag bolts or lag screws can be made of carbon steel, stainless steel, and can be hot-dip galvanized as needed to suit any project. It has a diameter of 1/4 inch to 5/8 inch and a length of 2-8 inches. Designed for strong fixing of wood to metal or concrete, it is mainly used in the construction field and is also commonly used in various indoor and outdoor projects.
Hanger Bolts
Hanger Bolts are also called hanging bolts and stud screws. One end has a coarse thread that can be screwed into the wood, and the other end has a mechanical thread (fine thread) that fits the standard nut. It has no head and needs to be clamped and installed with a double nut or tool. It is used for the transition between wood and metal.
Made of ordinary carbon steel or stainless steel, the surface can be galvanized to prevent rust and corrosion.
Size: 1/4 inch to 5/8 inch in diameter, 2-8 inches in length.
Application scenario
Furniture assembly: connect wooden table legs and metal brackets.
Mechanical fixation: transition connection between the motor base and the wooden platform.
Anchor Bolts
Anchor Bolts are also known as foundation bolts and foundation anchor bolts. They are divided into L-type anchor bolts that are pre-buried before concrete pouring and have strong pull-out resistance, and post-type anchor bolts such as expansion bolts and chemical anchor bolts (installed after drilling), which are used to fix the structure to concrete, masonry and other substrates.
The materials are carbon steel and stainless steel that meet the ASTM F1554 high-strength anchor bolt standard
Application scenarios
Building foundation: steel structure columns, bridge bearings.
Equipment fixing: tower crane, transformer base.
Expansion Bolts
expansion anchors are also called expansion screws .They are fasteners composed of bolts, expansion sleeves, nuts, washers, etc. They are post-bolts that are fixed by friction in the drilled hole through the expansion sleeve. They are a type of anchor bolt.
The material is mostly galvanized carbon steel, with a commonly used diameter of 6mm-20mm and a length of 50mm-300mm.
Application scenarios
Wall fixing: hanging air conditioners, shelves, guardrails.
Equipment installation: pipe brackets, solar panel bases.
Anchor bolts are special tools used to reinforce various buildings. They are mainly divided into two types: mechanical anchor bolts and chemical anchor bolts. Mechanical anchor bolts are stretched and fixed like springs. They are suitable for ordinary walls to install shelves and guardrails. They are cheap and quick to install. Chemical anchor bolts are bonded with strong glue. They are suitable for heavy-duty or easily broken walls. They are stronger but require the glue to dry. During construction, you need to see whether the wall is strong, how much weight it needs to bear, and whether the environment is humid. A high-quality and qualified anchor bolt can make your project stand for a hundred years, but wrong choices or quality problems will bring great safety hazards. When you are unsure, it is best to consult a professional to avoid unnecessary trouble.
Post time: May-08-2025